The present invention relates to the fabrication of semiconductor devices, particularly to self-aligned silicide (salicide) technology, and the resulting semiconductor devices. The present invention is particularly applicable to ultra large scale integrated circuit (ULSI) systems having features in the deep sub-micron regime.
As integrated circuit geometries continue to plunge into the deep sub-micron regime, it becomes increasingly more difficult to accurately form discreet devices on a semiconductor substrate exhibiting the requisite reliability. High performance microprocessor applications require rapid speed of semiconductor circuitry. The speed of semiconductor circuitry varies inversely with the resistance (R) and capacitance (C) of the interconnection system. The higher the value of the Rxc3x97C product, the more limiting the circuit operating speed. Miniaturization requires long interconnects having small contacts and small cross-sections. Accordingly, continuing reduction in design rules into the deep sub-micron regime requires decreasing the R and C associated with interconnection paths. Thus, low resistivity interconnection paths are critical to fabricating dense, high performance devices.
A common approach to reduce the resistivity of the interconnect to less than that exhibited by polysilicon alone, e.g., less than about 15-300 ohm/sq, comprises forming a multilayer structure consisting of a low resistance material, e.g., a refractory metal silicide, on a doped polycrystalline silicon layer, typically referred to as a polycide. Advantageously, the polycide gate/interconnect structure preserves the known work function of polycrystalline silicon and the highly reliable polycrystalline silicon/silicon oxide interface, since polycrystalline silicon is directly on the gate oxide.
Various metal silicides have been employed in salicide technology, such as titanium, tungsten, and cobalt. Nickel, however, offers particularly advantages vis-à-vis other metals in salicide technology. Nickel requires a lower thermal budget in that nickel silicide and can be formed in a single heating step at a relatively low temperature of about 250xc2x0 C. to about 600xc2x0 C. with an attendant reduction in consumption of silicon in the substrate, thereby enabling the formation of ultra-shallow source/drain junctions.
In conventional salicide technology, a layer of the metal is deposited on the gate electrode and on the exposed surfaces of the source/drain regions, followed by heating to react the metal with underlying silicon to form the metal silicide. Unreacted metal is then removed from the dielectric sidewall spacers leaving metal silicide contacts on the upper surface of the gate electrode and on the source/drain regions. In implementing salicide technology, it was also found advantageous to employ silicon nitride sidewall spacers, since silicon nitride is highly conformal and enhances device performance, particularly for p-type transistors. However, although silicon nitride spacers are advantageous from such processing standpoints, it was found extremely difficult to effect nickel silicidation of the gate electrode and source/drain regions without undesirable nickel silicide bridging and, hence, short circuiting, therebetween along the surface of the silicon nitride sidewall spacers.
Accordingly, there exists a need for salicide methodology enabling the implementation of nickel silicide interconnection systems without bridging between the nickel silicide layers on the gate electrode and the source/drain regions, particularly when employing silicon nitride sidewall spacers on the gate electrode.
An advantage of the present invention is a method of manufacturing a semiconductor device having nickel silicide contacts on a gate electrode and associated source/drain regions without bridging therebetween along insulative sidewall spacers, notably silicon nitride sidewall spacers.
Another advantage of the present invention is a semiconductor device having nickel silicide contacts on a gate electrode and on associated source/drain regions without bridging therebetween along insulative sidewall spacers, particularly silicon nitride sidewall spacers.
Additional advantages and other features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned by practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a method of manufacturing a semiconductor device, the method comprising: forming a silicon gate electrode, having opposing side surfaces, on a substrate with a gate insulating layer therebetween; forming an inner layer of silicon nitride sidewall, having a first refractive index at a thickness of about 450 xc3x85 to about 550 xc3x85, on the opposing side surfaces of the gate electrode; forming an outer layer of silicon nitride having a refractive index less than the first refractive index and less than about 1.95 and at a thickness of about 350 xc3x85 to about 450 xc3x85, on the inner layer of silicon nitride, the inner and outer layers of silicon nitride forming composite sidewall spacers; depositing a layer of nickel on the gate electrode and on the exposed substrate surfaces; and heating to react the layer of nickel with underlying silicon to form a layer of nickel silicide on the gate electrode and layers of nickel silicide on the exposed surfaces of the substrate.
Embodiments of the present invention include forming the first layer of nickel silicide with a refractive index of about 1.95 to about 2.05, e.g., about 2.05, and forming the second layer of silicon nitride with a refractive index of about 1.75 to about 1.93, wherein the second layer of silicon nitride contains more nitrogen and less silicon, particularly less silicon dangling bonds, than the first layer of silicon nitride, thereby preventing the formation of nickel silicide on the composite sidewall spacers and, hence, preventing nickel silicide bridging between the layer of nickel silicide on the gate electrode and the layers of nickel silicide on associated source/drain regions. Embodiments of the present invention further include forming an oxide liner on the opposing side surfaces of the gate electrode prior to forming the silicon nitride sidewall spacers, sputter etching in argon before depositing the layer of nickel to remove contamination and forming the nickel silicide layers at a temperature of about 400xc2x0 C. to about 600xc2x0 C.
Another aspect of the present invention is a semiconductor device comprising: a gate electrode, having opposing side surfaces and an upper surface, on a semiconductor substrate with a gate insulating layer therebetween; a composite silicon nitride sidewall spacer on each opposing side surface of the gate electrode, the compositie siliocn nitride sidewall spacer comprising: an inner layer of silicon nitride having a first refractive index and a thickness of about 450 xc3x85 to about 550 xc3x85; on one of the opposing side surfaces of the gate electrode; and an outer layer of silicon nitride, having a refractive index less than the first refractive index and less than about 1.95 and having a thickness of about 350 xc3x85 to about 450 xc3x85, on the inner layer of silicon nitride, a layer of nickel silicide on the upper surface of the gate electrode; and a layer of nickel silicide on the substrate surface adjacent each silicon nitride sidewall spacer. The outer layer of silicon nitride having the lower refractive index contains more nitrogen and less free silicon than the inner layer of silicon nitride, thereby preventing the formation of nickel silicide thereon and, hence, preventing bridging between the layer of nickel silicide on the gate electrode and layers of nickel silicide on the associated source/drain regions.
Additional advantages of the present invention will become readily apparent to those having ordinary skill in the art from the following detailed description, wherein embodiments of the present invention are described simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.